The present invention relates to a paraseismic device for the handling hood of a nuclear reactor.
It is known that in most cases nuclear reactors are surrounded by a protective caisson with thick concrete walls, sealed at its upper end by a slab having a series of tightly sealed passages, permitting access from the outer surface of the slab in the ambient atmosphere to the inside of the caisson, notably the reactor core, in order to carry out the various operations which are necessary. It is conventional practice to arrange on said slab one or several hoods, which serve to receive a reactor component and can either be removed from the latter for inspection or repair or can be introduced into the caisson for the replacement of a worn or damaged component. The connection between the hood body, generally in the form of a cylindrical enclosure with a vertical axis, displaceable on the surface of the slab by appropriate positioning means, and a passage provided in the said slab, is effected by means of a lock installed beneath the enclosure of the hood and having tight connecting means with the passage of the slab in order to ensure the necessary sealing.
Generally in nuclear reactors the enclosures of hoods have a relatively small diameter, of approximately 0.5 to 3 meters, compared with their height, which can be 25 meters, whilst the weight of the assembly can exceed 120 tonnes. Thus, in the case of earthquakes, the accelerations imposed on the hood lead to very large stresses at the connection between the lock and the slab and in the case of large shocks said stresses become completely unacceptable.